#### Answer

The domain of the given function is the set of all real numbers.

#### Work Step by Step

The denominator of a rational function cannot be $0$, hence $x^2+1$ should not be $0$.
However, the value of $x^2+1$ will never be equal to zero since the value of $x^2$ is always non-negative for all real numbers.
Thus, the domain of the given function is the set of all real numbers.